A liquid crystal display (LCD) typically has a back light section 1 which includes a synthetic resin diffusive plate (diffusive film) 3 and one or two synthetic resin prism lens 4 in front of light sources 2 such as fluorescent light tubes in the order mentioned, and an LCD section 6 including LCD elements in front of the back light section 1, as shown in FIG. 19. The light emitted from the light sources 2 is scattered while passing through the light diffusive plate 3 and collimated by the prism lens 4 to the liquid crystal (LC) elements of the LCD section 6, so that sufficient brightness of the LCD in the direction normal thereto is attained. Reference numeral 2a indicates a case for housing the light sources 2, and 1a a back cover unit.
Mounted on top of the prisms formed on the prism, lens 4 is a transparent synthetic resin protective film 8 for protecting the prism lens 4. The protective film 8 comprises on at least the back (facing the prism lens 4) thereof a rough surface 8a having micro protrusions/recesses to prevent Moire fringes that arises when prism lenses are stacked together, blur and glare pertinent to prism lenses, and to suppress inversion of light (which is a tendency that the brightness in oblique directions decreases rapidly as compared with the brightness in the direction normal to the prism lens).
However, a problem arises in such LCDs in that the protective film 8 can scratch ridges of the prisms 4a of prism lens 4 and leave scars 5 as shown in FIG. 20 if the protective film 8 is moved relative to the prism lens 4 in the right or left direction as shown in FIG. 21 due to a move during a manufacturing process assembling an LCD panel, or due to thermal expansions/contractions of the protective film 8 during the use of the LCD panel. These scars will prevent proper distribution of light and diminishes the commercial value of the prism lens 4.
In the examinations of the problem mentioned above, the inventors have found that the scars 5 are caused by the rough face 8a of the protective film 8 facing the prism lens 4, that is, the protrusions 9 of the rough surface 8a on the back of the protective film 8 scratches the ridges 4b of the prisms 4a of the prism lens 4, leaving scars 5 as shown in FIG. 21, when the protective film 8 and the prism lens 4 are moved to each other.
The invention is directed to overcome the above mentioned problem pertinent to prior art LCDs. It is therefore an object of the invention to provide a protective film for a prism lens that does not damage the ridges of the prisms of the prism lens,